It is random for everyone, group members included. Six players with the same 5 targets could potentially monopolize the zone. However, the sets of targets for each part are chosen from similar areas to help alleviate the run around when grouped.

“It is random for everyone, group members included. Six players with the same 5 targets could potentially monopolize the zone. However, the sets of targets for each part are chosen from similar areas to help alleviate the run around when grouped.”

If 6 members of a group have different targets they're going to monopolize the zone MORE then if every member of the group was looking for the same mobs. Because now they have to kill MORE mobs to satisfy everybody's quests.example Everybody needs 5 each of mobs a, b, c, d and e. That's 25 mobs for the 6 peopleIf they each need 5 mobs, but split between a, b, c, d, e, f, g, h, i and j.. that is50 mobs for the same 6 people.

“I believe I searched the entire zone, including the two islands. However, never found any mudhoppers.”

They're frogs. Look in the Muddy Lagoon, which is the southernmost part of the zone (-68, 18, 598), and I think I recall seeing some frogs on the Korascian Cliffs, which are just west of the Terrak temple (424, 51, 6).